1. Field of Disclosure
The present disclosure relates to new methods for making multi-phase nanocomposite materials and, more specifically, to nanocomposite ceramics from inexpensive starting materials and reagents. These multi-phase oxide ceramics powders are produced with very small (typically less than 100 nanometers) nano phase domains. Such materials have superior resistance to grain growth upon heating and are more readily processed into very fine structured multi-phase ceramics with superior mechanical, catalytic and optical properties.
2. Background of the Disclosure
There are two main reasons for the recent interest in nanocomposite ceramics. Firstly, these materials can exhibit enhanced properties as compared with the corresponding coarse-grained ceramic composites or with single-phase nanostructured ceramics. The range of properties that can be influenced by the structure of nanocomposite ceramics include the mechanical, chemical, thermal, electrical, magnetic and optical properties. Secondly, nanocomposite ceramics can exhibit greatly enhanced microstructure stability as compared with single-phase nanostructured ceramics. This can be important for materials that will experience high temperatures during processing and/or service. This microstructure stability arises due to grain-boundary pinning and/or lower coarsening rates for phase domains than for grains within a domain. Both of these effects are enhanced in nanocomposites with fine, uniformly dispersed phase domains. The production of nanocomposite ceramics with fine uniform phase domains is particularly challenging due to the need to control both the microstructure length scales and the elemental distributions. Many of the conventional synthetic methods for producing ceramics (e.g. precipitation, hydrothermal, reflux, thermal decomposition, etc.) are not amenable to such control because of the reaction/nucleation rates involved and/or the physical/chemical properties of the components. Although various different approaches have been developed to overcome these limitations, these typically involve complex equipment, extremely high temperatures and/or low yields, resulting in high production cost.
Sol-gel methods utilize lower temperatures and offer a greater degree of control over elemental ratios and homogeneity than most of the methods mentioned above. A potential drawback is that effective sol-gel processing requires precise control of synthesis conditions and, usually, expensive organometallic precursors. Thus, sol-gel processed nanocomposite ceramics can also be expensive.
A less costly derivative of the sol-gel technique is esterification sol-gel (ESG) processing, which utilizes esterification of less expensive precursors to create a similar sol-gel environment under a wider range of synthesis conditions. This ESG approach has been used recently for the synthesis of catalytic nanoparticles and metal oxide/polymer nanocomposites (D T Jiang and A. K. Mukherjee, “Synthesis of Y2O3—MgO Nanopowder and Infrared Transmission of the Sintered Nanocomposite,” Proceedings of SPIE—Intl. Soc. for Optical Engr., 703007 I-A5 (2008)). There it is reported that the microstructure evolved with increasing heat treating temperature. Taking advantage of high heating rates, spark plasma sintering (SPS) technique was used to sinter the nanopowder, which was said to result in a fully dense nanocomposite with grain size below 100 nm.